Respirators are used in a variety of hazardous environments, such as paint booths, grain storage facilities, laboratories, and manufacturing facilities in which contaminants are present. Respirator masks are typically adapted to receive a variety of filter cartridges or air supply connectors to provide a source of breathable air to the wearer so that the same face mask design may be used in a variety of different hazardous environments.
The two major classes of respirator systems are positive and negative pressure respirators. A positive pressure respirator typically includes a positive pressure air source such as an external pump or pressurized vessel that force clean air into the face mask. The positive pressure air source provides an excess of clean, breathable air to a face mask. The net positive pressure in the face mask due to the positive pressure air source prevents ambient air from being drawn around the face seal of the mask.
One type of positive pressure air source for use with a positive pressure respirator system is a powered air purifier respirator (PAPR). A powered air purifying respirator typically includes a breathing tube from the face mask to a battery powered blower unit worn by the user. The blower unit typically contains a filter to remove contaminants from the ambient air. Powered air purifying respirators have the advantage of allowing the user to move freely, without being tethered to an air line. However, powered air purifying respirators tend to be more expensive than continuous flow respirator systems. Additionally, powered air purifying respirators are battery operated and consequently can only be used for a limited period of time. Finally, powered air purifying respirators generally require a large bore diameter breathing tube (approximately 25 mm), because battery operated blowers generally can not generate sufficient pressure for a smaller bore diameter breathing tube. These large bore diameter breathing tubes can be cumbersome to the user.
Alternatively, the positive pressure air source may be a compressor or pressure vessel connected to the user by an air line. Typically, these systems include a filter at the compressor to provide the user with breathable air. However, for some applications, the air line may restrict the user's ability to perform certain functions. Additionally, the air line may get kinked or the supply of pressurized air may be accidentally terminated, potentially exposing the users to contaminants.
The other major class of respirators are called negative pressure respirators because the user's inhalation draws air through a filter cartridge into the face mask. The filter cartridge may contain a variety of filtering elements, such as blown microfibers or carbon-based systems for gas and vapor protection. Negative pressure respirators have the advantage of not requiring the wearer to drag an air line or to wear an expensive powered-air purifying respirator system. The disadvantage of negative pressure respirators is that the user must utilize lung power to draw air through the filter media and the resulting negative pressure in the face mask can potentially allow contaminants to be drawn in around the face seal. Additionally, using respiratory lung power to draw air through the filter media tends to heat up the face mask, creating discomfort for the wearer. Consequently, negative pressure respirators generally have a lower protection level than positive pressure respirators.